The identification of materials having an absorbent substrate is of general importance in industrial manufacture. The state of the art includes many procedures for identifying piece goods during the manufacturing process. Such identification offers to the manufacturer, inter alia, the advantage of improved production control as compared with an imprint applied only to the finally manufactured product. Also, the user of the product has advantages due to a permanent identification, for example, when associating individual items with suppliers, and determination of delivery times.
Inkjet printers are frequently employed in the art for the labeling of relatively large areas having an absorbent substrate, for example, paper, wood, ceramics. For this purpose, and for technically similar systems, a large array of suitable colorants is available from various manufacturers. Many of these colorants contain soluble organic dyes which lack thermostability. Suspensions of colored pigments cannot be utilized in this identification technique because they are incompatible with the devices used in applying the marks.
It is known in accordance with Japanese Laid-Open Application Sho 60/49073 and Japanese Published Application 75/6802 to utilize solutions of cobaltous thiocyanate as blue inks which can be removed with water. Japanese Laid-Open Application Sho 63/30572 discloses the use of copper-or cobalt-chelate complexes as inks. However, these inks exhibit low compatibility with the identified material when subjected to a thermal aftertreatment.
German Patent Application P 39 02 225, which is not a prior publication, describes a method for the identification of absorbent material with a thermostable colorant characterized by applying a cobalt salt solution to an absorbent material and then stabilizing the thus-applied identification mark by a thermal aftertreatment at temperatures higher than 400.degree. C. However, the cobalt salt solution applied according to the German Patent Application P 39 02 225 is not very legible immediately after application to the absorbent material. This holds true, in particular, for identification marks applied to absorbent material which are other than white.
It is therefore desired to have for the identification of absorbent material a thermostable colorant and process of using same, wherein the colorant is very readily readable immediately after application as well as after a thermal treatment at temperatures higher than 400.degree. C. Such identification marks can be used to control manufacturing of the end product or intermediate products which are subjected to elevated temperatures.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.